A technology of searching for a corresponding point between a baseline image and a reference image obtained by imaging the same object (subject) with two imaging apparatuses from different view points, for the baseline image and the reference image is known. In this technology, for example, a disparity with respect to the same object is obtained based on a correlation degree by performing a correlation computation through SAD (Sum of Absolute Difference) computation method, or the like.
Furthermore, for example, a plurality of images having different resolutions are generated to obtain a hierarchical structure by resolution for the baseline image and the reference image, and processing in which the correlation computation is sequentially repeated from the upper level layer of lower resolution toward the lower level layer of higher resolution is known. In such processing, the time required for the computation processing to the lowermost layer having the highest resolution can be reduced since a search region in the next layer is set based on the disparity obtained in the upper level layer of lower resolution.
It is known that highly accurate computation results can be obtained regardless of disturbance, and the like by adopting a POC (Phase-Only Correlation) computation method in the search processing of the corresponding point. However, the processing amount of the computation including Fourier transformation, extraction of phase information, and the like is large in the POC computation method, which may lead to lowering in the operation efficiency, and the like due to longer processing time.
In the search processing of the corresponding point associated with each point, therefore, a technology of calculating the rough disparity through the SAD computation method, and setting the layer of the resolution in which the computation processing using the POC computation method is started and the search region based on the rough disparity is proposed (e.g., Japanese Patent Application Laid-Open No. 2008-209275, etc.). In this technology, the search processing of the corresponding point can be carried out at high precision and at high speed.